The first set of proposed experiments is designed to compare and contrast synaptogenesis occurring in a regenerating system, the goldfish retinotectal system, with lesion induced reorganization occurring by collateral sprouting in a non-regenerating system, the rat interpeduncular nucleus (IPN). The specific issues are related to a comparison of the factors regulating reestablishment of specific numbers and patterns of connections by regenerating goldfish retinal axons with the factors regulating collateral sprouting and reactive reinnervation by intact neurons after lesions in mammalian CNS. This information is essential in order to predict the functional consequences of lesion induced synaptogenesis in the adult CNS. A second goal is to determine those cellular processes which distinguish the response of the rat retinal ganglion cell, axotomized and induced to elongate its axon via implantation techniques, from the axotomized but non-regenerating rat retinal ganglion cell and from the regenerating goldfish retinal ganglion cell. These studies should contribute to an elucidation of the processes which account for the robust and directed growth of the axotomized goldfish optic axons and those which account for the normal failure of this growth in the axotomized mammalian central axons.